1. Field of the Invention
The present invention relates to a chip resistor and to a manufacturing method of a chip resistor.
2. Description of the Related Art
FIG. 13 illustrates a chip resistor X2 as an example of conventional chip resistor. The chip resistor X2 includes a substrate 91, a pair of electrodes 92, a resistive layer 93, and a protective layer 94.
The substrate 91 is made of an insulating material. The electrodes 92 are provided spaced apart from each other on the substrate 91. Each electrode 92 has a plating layer 921 which is formed along a part of the top surface, the side surface and a part of the bottom surface of the substrate 91 shown in FIG. 13. The purpose of the plating layer 921 is to improve solderability in a mounting state of the chip resistor X2. In other words, the plating layer 921 is a means for ensuring good solderability in the mounting state of the chip resistor X2. The resistive layer 93 is formed on the top surface of the substrate 91 shown in FIG. 13 and electrically connected to the pair of electrodes 92. The protective layer 94 covers the resistive layer 93. On the bottom surface of the substrate 91 shown in FIG. 13, the portions of the pair of electrodes 92 are arranged respectively in the vicinity of ends, in direction x, of the substrate 91 shown in FIG. 13. Thus, the bottom surface of the substrate 91 is exposed at the region between the pair of electrodes 92. As a result, on the bottom surface of the substrate 91 shown in FIG. 13, there forms a distinctive level difference between each of the electrodes 92 and the exposed region of the bottom surface of the substrate 91. This type of chip resistor is disclosed in JP-A-2008-270519, for example.
In a mounting process, the chip resistor X2 having the above configuration is placed on a circuit board, with the bottom surface of the substrate 91 shown in FIG. 13 facing to the circuit board. In the chip resistor X2, the bottom surface of the substrate 91 shown in FIG. 13 is i.e. the mount side surface.
In the chip resistors X2 having the above configuration, there is a pressing demand for smaller sizes and thinner profiles, with a view to increasing the mounting efficiency of the electric circuitry of which the chip resistor X2 is a constituent.
In the chip resistor X2, however, the substrate 91 loses mechanical strength when the thickness thereof is reduced in terms of achieving, for instance, a thinner profile. When the chip resistor X2 with the thickness of the substrate 91 reduced is subjected to load particularly in the mounting process, the substrate 91 may crack at the portion between the electrodes 92 or the substrate 91 may be damaged through bending or the like. This is because the substrate 91 of the chip resistor X2, mounted onto the circuit board as stated above, is supported at its both ends by the two electrodes 92, while there forms a relatively large gap between the circuit board and the exposed region of the bottom surface of the substrate 91 shown in FIG. 13. As noted before, the distinctive level difference between each of the electrodes 92 and the exposed region of the bottom surface of the substrate 91 shown in FIG. 13 is formed in the chip resistor X2.
Any of the above occurrences may give rise to significant errors in the resistance value of the chip resistor X2, or may lead to deviations in the specifications of the electric circuitry of which the chip resistor X2 is a constituent, among other problems.